1. Field of the Invention
The present invention concerns a loudspeaker gain correction method for a "hands-free" telephone terminal or for an audioconference telephone terminal.
2. Description of the Prior Art
A hands-free telephone set or telephone terminal includes a sound pick-up device with one or more microphones, a sound output device with one or more loudspeakers and transmit and receive signal processing circuits. These circuits include an acoustic echo canceller, an electric echo canceller and a gain variation device for attenuating the signals transmitted during a telephone conversation to prevent the Larsen effect. The attenuation is determined by the dominant transmission direction and by the performance of the echo cancellers.
A user controls the listening level by modifying the loudspeaker gain. The higher the chosen listening level, the less attenuation is applied to the non-dominant transmission direction. This attenuation is called the stability gain and takes a positive value less than unity. An excessively high attenuation, for example greater than 10 dB, would make listening more uncomfortable for the local user and for the other party, called as a remote user. The latter perceive variations in the levels of the speech signals transmitted and have the sensation of a half-duplex communication. When choosing the listening level, the local user is most sensitive to the sound intensity of the voice of the remote user and chooses an excessively high listening level. Unknown to them, this then causes a deterioration of the overall quality of the audioconference, in particular through a progressively more accentuated sensation of half-duplex communication. This sensation is all the stronger for the remote user if he is using the handset of his telephone.